An outbreak of gummosis of mango trees caused by Lasiodiplodia theobromae in Guangxi, south China.
Li Q. L., Guo T. X., Pan Z. B., Huang S. P., Mo J. Y., Ning P., Hsiang T.
Author Affiliation: Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning, Guangxi, 530007, China.
Plant Disease 97 :690
Abstract : In May 2012, a total of 2250 mango trees in nine orchards were surveyed in 5 counties in Guangxi Province, China. An outbreak of gummosis was observed in the province involving more than 30?000 ha, with an average of 50% disease incidence (DI) and a maximum of 70% in some orchards. Until then, gummosis had been considered a common but not serious disease. In 2012, high temperatures in April and extensive rain in May favoured disease development. Infected plants showed abundant gum secretion from branches, stems and main trunks. Some branches died from the disease. During the early stages of infection, branches or stems turned brown, which was followed by xylem necrosis and exudation of a milky sap. The sap turned yellow and finally formed amber gum within several days. The gum appeared as small droplets, increasing in number, later covering most of the branches and the trunk. Bark cracking was evident under severe conditions. On potato dextrose agar, isolates with similar morphology were consistently recovered from symptomatic plant tissues. Cultures were grey with an irregularly distributed, fast-growing, and fluffy aerial mycelium, showing a dark underside as the colony changed from greenish to black after 5 days at 28°C. After one month, cultures produced globose pycnidia. Conidia were elliptical and hyaline when immature, becoming dark brown and one-septate. The fungus was identified as L. theobromae based on morphological and cultural characteristics. The rDNA internal transcribed spacer region of one isolate showed 100% identity to L. theobromae (GenBank HM346876.2) In China, the disease was observed in the 1990s in Hainan Province, and the causal agents were identified as L. theobromae and Colletotrichum gloeosporioides based on morphological observation. This is thought to be the most severe outbreak of gummosis reported from China.